Cathode for metal-air battery including spaces for accommodating metal oxides formed during discharge of metal-air battery and metal-air battery including the same

ABSTRACT

Provided is a metal-air battery including a cathode having a space which may be filled with a metal oxide formed during a discharge of the metal-air battery and thus having improved energy density and lifespan. The cathode for the metal-air battery includes a plurality of cathode materials, a plurality of electrolyte films disposed on surfaces of the plurality of cathode materials, and a plurality of spaces which are not occupied by the plurality of cathode materials and the plurality of electrolyte films. A volume of the plurality of spaces may be greater than or equal to a maximum space of a metal oxide formed during a discharge of the metal-air battery.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/795,841, filed on Oct. 27, 2017, which claims priority to KoreanPatent Application No. 10-2016-0144480, filed on Nov. 1, 2016, andKorean Patent Application No. 10-2017-0121876, filed on Sep. 21, 2017,and all the benefits accruing therefrom under 35 U.S.C. § 119, thecontent of which in its entirety is herein incorporated by reference.

BACKGROUND 1. Field

Embodiments set forth herein relate to a cathode for a metal-air batteryand a metal-air battery including the same, and more particularly, to acathode having a space which may be filled with a metal oxide generatedduring a discharge, and a metal-air battery including the cathode andthus having improved energy density and lifespan.

2. Description of the Related Art

A metal-air battery includes a negative electrode capable ofintercalating/deintercalating ions and a positive electrode that usesoxygen in the air as an active material. In the metal-air battery,reduction and oxidation reactions of oxygen received from an outsideoccur in the positive electrode, oxidation and reduction reactions ofthe metal occur in the negative electrode, and chemical energy generatedis then extracted as electrical energy. For example, the metal-airbattery absorbs oxygen when discharging and emits oxygen when charging.As described above, since the metal-air battery uses oxygen in the air,the energy density of the metal-air battery may be greater than those ofother batteries. For example, the metal-air battery may have an energydensity several times higher than that of a conventional lithium ionbattery.

In addition, the metal-air battery has a low probability of igniting dueto an abnormally high temperature, and the metal-air battery is onlyoperated by intercalation and deintercalation of oxygen without using aheavy metal, such that the metal-air battery is highly stable and lesslikely to harm the environment. Due to such various desiredcharacteristics, research into the metal-air battery is currently beingperformed more and more.

SUMMARY

According to an embodiment, a cathode for a metal-air battery includes aplurality of cathode materials, a plurality of electrolyte filmsdisposed on surfaces of the plurality of cathode materials, and a spacewhich is not occupied by the plurality of cathode materials and theplurality of electrolyte films. A volume of the space is greater than orequal to a maximum volume of a metal oxide formed during a discharge ofthe metal-air battery.

For example, the plurality of electrolyte films may be formed of anorganic material.

For example, the volume of the space may be equal to or less than 120%of the maximum volume of the metal oxide.

The plurality of cathode materials each may have a flat panel shape, andmay be arranged in parallel to each other.

Each of the plurality of cathode materials may include a first surfaceand a second surface which are opposite to each other, and a thirdsurface and a fourth surface which are opposite to each other and extendbetween the first surface and the second surface. Each of areas of thethird surface and the fourth surface is smaller than each of areas ofthe first surface and the second surface. The plurality of cathodematerials are arranged in a way such that the first and second surfacesof two adjacent cathode materials face each other.

The plurality of electrolyte films may be disposed at least on the firstand second surfaces of each of the plurality of cathode materials.

A width of the space may be defined as a distance between electrolytefilms facing each other between two adjacent cathode materials, and thewidth of the space when the metal oxide is not formed may be greaterthan about 20 nm.

For example, each of the plurality of cathode materials may have athickness of about 10 nm or less, and each of the plurality ofelectrolyte films may have a thickness of about 10 nm or less.

For example, each of the plurality of cathode materials may have acylindrical shape, and each of the plurality of electrolyte films may bedisposed on an outer circumferential surface of a corresponding one ofthe plurality of cathode materials.

For example, each of the plurality of cathode materials may includecarbon nanotubes.

For example, each of the plurality of cathode materials may have adiameter of about 150 nm or less, and each of the plurality ofelectrolyte films may have a thickness of about 10 nm or less.

For example, the plurality of cathode materials may be arranged at adensity greater than about 10⁹/cm².

According to an embodiment, a metal-air battery includes a cathodehaving a structure as described above, an anode metal layer configuredto supply metal ions to a plurality of cathode materials of the cathode,and a gas diffusion layer configured to supply oxygen to the pluralityof cathode materials.

Each of a plurality of electrolyte films of the cathode may include afirst electrolyte portion disposed on a top surface of the anode metallayer, and a second electrolyte portion extending from the firstelectrolyte portion to a surface of one of the plurality of cathodematerials.

The plurality of cathode materials may be arranged in a way such thateach of a first end portions thereof is in contact with a correspondingone of the first electrolyte portions and second end portions thereofare in contact with the gas diffusion layer.

The metal-air battery may further include a third electrolyte portionwhich transmits metal ions and blocks moisture and oxygen, wherein thethird electrolyte portion is disposed between the first electrolyteportion and the anode metal layer.

According to another embodiment, a cathode for a metal-air batteryincludes a cathode layer which uses oxygen as an active material, aplurality of holes vertically defined through the cathode layer, aplurality of electrolyte films disposed on inner walls of the cathodelayer, which define the plurality of holes, and a plurality of spaces ofthe plurality of holes which are surrounded by the plurality ofelectrolyte films. A volume of the plurality of spaces may be greaterthan or equal to a maximum volume of a metal oxide formed during adischarge of the metal-air battery.

For example, the plurality of holes may be arranged in the cathode layerat a density greater than about 10⁹/cm².

The volume of the plurality of spaces may be equal to or less than 120%of the maximum volume of the metal oxide.

An area of a cross-section of the space in each of the plurality ofholes when the metal oxide is not formed may be greater than an area ofa cross-section of the metal oxide on the inner walls of the cathodelayer when the metal oxide is formed.

For example, each of the plurality of electrolyte films on the innerwalls of the cathode layer when the metal oxide is not formed may have athickness of about 10 nm or less.

For example, each of the plurality of holes may have a polygonal orround shape.

According to another embodiment, a metal-air battery includes a cathodehaving a structure as described above, an anode metal layer facing abottom surface of a cathode layer of the cathode; and a gas diffusionlayer which supplies oxygen to the cathode layer and faces a top surfaceof the cathode layer.

Each of a plurality of electrolyte films of the cathode may include afirst electrolyte portion disposed on a top surface of the anode metallayer; and a second electrolyte portion extending from the firstelectrolyte portion to a corresponding one of the inner walls of thecathode layer.

The cathode layer may be arranged in a way such that the bottom surfaceof the cathode layer is in contact with the first electrolyte portionand the top surface of the cathode layer is in contact with the gasdiffusion layer.

The metal-air battery may further include a third electrolyte portionwhich transmits metal ions and blocks moisture and oxygen, wherein thethird electrolyte portion is disposed between the first electrolyteportion and the anode metal layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other features will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a structure of a metal-airbattery according to an embodiment;

FIG. 2 is a schematic cross-sectional view of a structure of a metal-airbattery according to an alternative embodiment;

FIG. 3 is a cross-sectional view illustrating a metal oxide generatedduring a discharge operation of the metal-air battery of FIG. 1 , and achange in the location of an electrolyte film caused by the metal oxide;

FIG. 4 is a schematic cross-sectional view of a structure of a metal-airbattery according to another alternative embodiment;

FIG. 5 is a schematic partial perspective view of a cathode for ametal-air battery according to an embodiment;

FIG. 6 is a schematic partial perspective view of a cathode for ametal-air battery according to an alternative embodiment;

FIG. 7 is a cross-sectional view illustrating a metal oxide generatedduring a discharge operation of the metal-air battery of FIG. 6 , and achange in the location of an electrolyte film caused by the metal oxide;

FIG. 8 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment;

FIG. 9 is a cross-sectional view illustrating a metal oxide generatedduring a discharge operation of the metal-air battery of FIG. 8 , and achange in the location of an electrolyte film caused by the metal oxide;

FIG. 10 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment;

FIG. 11 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment;

FIG. 12 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment;

FIG. 13 is a cross-sectional view illustrating a metal oxide generatedduring a discharge operation of the metal-air battery of FIG. 12 , and achange in the location of an electrolyte film caused by the metal oxide;

FIG. 14 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment;

FIGS. 15 to 17 are graphs showing characteristics of the metal-airbattery of FIG. 6 ; and

FIGS. 18 to 20 are graphs showing characteristics of the metal-airbattery of FIG. 14 .

DETAILED DESCRIPTION

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which various embodiments areshown. This invention may, however, be embodied in many different forms,and should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. Like reference numerals refer tolike elements throughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “Or” means “and/or.” As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

Hereinafter, embodiments of a cathode for a metal-air battery and ametal-air battery including the same will be described in detail withreference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a structure of a metal-airbattery 100 according to an embodiment.

Referring to FIG. 1 , a cathode for the metal-air battery 100 accordingto an embodiment may include a plurality of cathode materials 102 whichuse oxygen as an active material and are spaced apart from each other,electrolyte films 103 disposed on surfaces of the plurality of cathodematerials 102, and spaces 105. In such an embodiment, spaces 105 aredefined in the cathode by the plurality of cathode materials 102 and theelectrolyte films 103. The metal-air battery 100 may further include ananode metal layer 101 facing first end portions of the plurality ofcathode materials 102, and a gas diffusion layer 104 facing second endportions of the plurality of cathode materials 102 and which suppliesoxygen to the plurality of cathode materials 102. The plurality ofcathode materials 102 may be generally regularly disposed such thatsecond end portions thereof are in contact with a surface of the gasdiffusion layer 104. plurality of cathode materials Here, the regularlydisposing of the plurality of cathode materials 102 should not beunderstood to mean that the distances between adjacent cathode materials102 among the plurality of cathode materials 102 are exactly the same,and may be understood to mean that the plurality of cathode materials102 are generally regularly distributed on the surface of the gasdiffusion layer 104 in consideration of an error in a manufacturingprocess.

The anode metal layer 101 may intercalate or deintercalate metal ions.In one embodiment, for example, the anode metal layer 101 includes or isformed of lithium (Li), natrum (Na), zinc (Zn), potassium (K), calcium(Ca), magnesium (Mg), iron (Fe), aluminum (Al), or an alloy thereof.

The electrolyte films 103 transfer metal ions to the plurality ofcathode materials 102. In an embodiment, each of the electrolyte films103 may include an electrolyte formed by dissolving a metal salt in asolvent, to transfer metal ions to the plurality of cathode materials102. In such an embodiment, the electrolyte may include an organicmaterial containing a polymer and may be manufactured to be in aflexible or bendable solid state. In such an embodiment, the electrolytemay include a polymer-based electrolyte, an inorganic electrolyte, or acomposite electrolyte which is a mixture thereof. In such an embodiment,the metal salt may include a lithium salt such as LiN(SO₂CF₂CF₃)₂,LiN(SO₂C₂F₅)₂, LiClO₄, LiBF₄, LiPF₆, LiSbF₆, LiAsF₆, LiCF₃SO₃,LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, LiN(SO₃CF₃)₂, LiC₄F₉SO₃, LiAlCl₄, or LiTFSI(Lithium bis(trifluoromethanesulfonyl)imide), for example. In such anembodiment, another metal salt such as AlCl₃, MgCl₂, NaCl, KCl, NaBr,KBr, CaCl₂), or the like may be added to the lithium salt describedabove. The solvent may be any organic solvent material capable ofdissolving the lithium salt and the metal salt described above.

In an embodiment, each of the electrolyte films 103 may further includea separator that prevents transmission of oxygen and has a property ofconducting metal ions. The separator may be a polymer-based separatorwhich is bendable. In one embodiment, for example, the separator may bepolymeric nonwoven fabric such as polypropylene nonwoven fabric orpolyphenylene sulfide nonwoven fabric, a porous film formed ofolefin-based resin such as polyethylene or polypropylene, or the like.The separator and the electrolyte may be disposed or formed in differentlayers. In an embodiment, where the separator is a porous separator, theseparator and the electrolyte may be in a same single layer in each ofthe electrolyte films 103 by impregnating pores of the porous separatorwith the electrolyte.

The plurality of cathode materials 102 may include a carbon-basedmaterial or various conductive organic materials. In one embodiment, forexample, the plurality of cathode materials 102 may include carbonblack, graphite, graphene, activated carbon, carbon fiber or carbonnanotubes, for example.

The gas diffusion layer 104 absorbs oxygen in the air and provides theoxygen to the plurality of cathode materials 102. In an embodiment, thegas diffusion layer 104 may have a porous structure to smoothly diffuseoxygen from the outside. In one embodiment, for example, the gasdiffusion layer 104 may include carbon paper, carbon cloth, or carbonfelt using carbon fiber, or may include a sponge foam metal or a metalfiber mat. Alternatively, the gas diffusion layer 104 may include aflexible porous material having non-conductive properties, such asnonwoven fabric. In an alternative embodiment, the plurality of cathodematerials 102 may be porous to function as a gas diffusion layer, andthe gas diffusion layer 104 may be omitted in this case.

Referring back to FIG. 1 , each of the electrolyte films 103 may includea first electrolyte portion 103 a on a top surface of the anode metallayer 101, and a second electrolyte portion 103 b extending from thefirst electrolyte portion 103 a to a surface of each of the plurality ofcathode materials 102. Thus, the electrolyte films 103 may extend fromthe top surface of the anode metal layer 101 to the surfaces of theplurality of cathode materials 102. The plurality of cathode materials102 may not be in direct contact with the anode metal layer 101 and thefirst end portions thereof may be in contact with the first electrolyteportions 103 a of the electrolyte films 103. The second end portions ofthe plurality of cathode materials 102 may be in direct contact with thegas diffusion layer 104.

In an embodiment, as shown in FIG. 1 , the anode metal layer 101 and thegas diffusion layer 104 each have a flat panel form and are arranged inparallel to each other, and the plurality of cathode materials 102 arearranged between the anode metal layer 101 and the gas diffusion layer104 to be perpendicular to the top surface of the anode metal layer 101.However, FIG. 1 merely illustrates a structure of the anode metal layer101 and the gas diffusion layer 104 at an embodiment. The structures ofthe anode metal layer 101 and the gas diffusion layer 104 are notlimited to those illustrated in FIG. 1 and may be variously modifiedaccording to a purpose and form of the metal-air battery 100.

FIG. 2 is a schematic cross-sectional view of a structure of a metal-airbattery 100 a according to an alternative embodiment.

Referring to FIG. 2 , in an embodiment, the metal-air battery 100 a mayfurther include a third electrolyte portion 103 c between the anodemetal layer 101 and the first electrolyte portion 103 a. The thirdelectrolyte portion 103 c may transmit metal ions and block moisture andoxygen to protect the anode metal layer 101. Thus, the third electrolyteportion 103 c may function as an electrolyte, a separator and aprotecting film. In an embodiment, the third electrolyte portion 103 cmay include a solid electrolyte or a polymeric electrolyte. In oneembodiment, for example, the third electrolyte portion 103 c may includeor be formed of LTAP (Li_(1+x)Ti_(2−x)Al_(x)(PO₄)₃). The anode metallayer 101 and the third electrolyte portion 103 c may both be referredto as a protective anode.

The metal-air batteries 100 and 100 a having the structures describedabove may generate electricity using oxidation and reduction of a metal.In one embodiment, for example, where the metal of the anode metal layer101 is lithium (Li), electricity is generated through a reaction oflithium (Li) and oxygen to generate a lithium oxide (e.g., Li₂O₂) duringdischarge. Conversely, a lithium metal is reduced from the lithium oxideto generate oxygen during charging. Alternatively, other various metalsmay be used as the metal of the anode metal layer 101, and reactionprinciples thereof may be the same as those of the metal-air batteryincluding lithium.

In an embodiment, when each of the metal-air batteries 100 and 100 a ischarged, empty spaces 105 which are not occupied by the plurality ofcathode materials 102 and the electrolyte films 103 are formed in thecathode. In other words, second electrolyte portions 103 b facing eachother on the surfaces of two adjacent cathode materials 102 are spacedapart from each other. A metal oxide such as Li₂O₂ may be formed betweenthe surfaces of the plurality of cathode materials 102 and theelectrolyte films 103 during discharge, such that the electrolyte films103 may be pushed away from the surfaces of the plurality of cathodematerials 102. In an embodiment, due to the spaces 105, the electrolytefilms 103 may be retained inside the cathode without leaking to theoutside of the cathode.

FIG. 3 is a cross-sectional view illustrating a metal oxide 106 formedduring a discharge operation of the metal-air battery 100 of FIG. 1 ,and a change in the locations of the electrolyte films 103 caused by themetal oxide 106.

Referring to FIG. 3 , during the discharge operation of the metal-airbattery 100, metal ions from the anode metal layer 101 to theelectrolyte films 103 react with oxygen supplied from the gas diffusionlayer 104 and electrons provided from the plurality of cathode materials102 to generate the metal oxide 106. When the discharge operation isconducted continuously, the metal oxide 106 is grown on surfaces of theplurality of cathode materials 102. Thus, the metal oxide 106 is formedbetween the surfaces of the plurality of cathode materials 102 and theelectrolyte films 103, and the electrolyte films 103 are pushed out bythe metal oxide 106 from the surfaces of the plurality of cathodematerials 102. In the current embodiment, the spaces 105 have volumeenough to accommodate the electrolyte films 103 therein without causingthe electrolyte films 103 to be discharged to the outside of the cathodeeven when the discharge operation is completed and thus the metal oxide106 is a maximum volume.

However, when the spaces 105 are extremely wide, the volume of themetal-air battery 100 may be increased. Thus, the spaces 105 may bedesigned to have an appropriate size by taking into account a thicknessof the metal oxide 106 to be formed during the discharge operation. Forexample, the spaces 105 may be designed such that the volume thereofwhen the metal oxide 106 is not generated is the same as or is 5, 10, or20% greater than that of the metal oxide 106 generated when thedischarge operation is completed. In other words, the volume of thespaces 105 may be 100 to 200% greater than a maximum volume of the metaloxide 106.

In general, the metal oxide 106 is a dielectric having an insulatingproperty. The metal oxide 106 having the insulating property may blockelectricity generated during formation of the metal oxide 106 fromflowing to the plurality of cathode materials 102. Thus, when the metaloxide 106 between the plurality of cathode materials 102 and theelectrolyte films 103 is extremely thick, the metal-air battery 100 mayhave reduced performance. Accordingly, in an embodiment, the metal-airbattery 100 may be driven such that the thickness of the metal oxide 106formed on the surfaces of the plurality of cathode materials 102 doesnot exceed about 10 nanometers (nm) during the discharge operation.Thus, in an embodiment, a width of the spaces 105 may be selected to beat least about 20 nm or more. In other word, the distance between thesecond electrolyte portions 103 b facing each other on the surfaces oftwo adjacent cathode materials 102 may be about 20 nm or more when themetal-air battery 100 is completely charged. Ideally, the sizes of allthe spaces 105 between the plurality of cathode materials 102 may beequally about 20 nm but an average size of a large number of spaces 105may be about 20 nm when an error in a manufacturing process isconsidered.

FIG. 4 is a schematic cross-sectional view of a structure of a metal-airbattery according to another alternative embodiment.

In an embodiment, as shown in FIGS. 1 and 3 , the first electrolyteportion 103 a of each of the electrolyte films 103 may be flat and thesecond electrolyte portion 103 b thereof may have a uniform thickness.In an alternative embodiment, as illustrated in FIG. 4 , a top surfaceof a first electrolyte portion 103 a between two adjacent cathodematerials 102 may have a concave curved surface and a thickness of asecond electrolyte portion 103 b may increase in a downward direction.

In such an embodiment of the metal-air battery, in which an empty spaceis defined in the cathode, an electrolyte of each of electrolyte films103 does not leak to the outside of the metal-air battery due to a metaloxide 106 formed during a discharge operation, thereby securing stablecharging/discharging reversibility. Thus, a number of times ofcharging/discharging may be increased, and the lifespan of the metal-airbattery may be increased. In such an embodiment, since the electrolytefilms 103 are disposed over surfaces of a plurality of cathode materials102, areas of contact between the plurality of cathode materials 102 andthe electrolyte films 103 are sufficiently large, and thus, an energydensity of the metal-air battery may increase with less amount ofelectrolyte.

FIG. 5 is a schematic partial perspective view of a cathode for ametal-air battery according to an embodiment.

Referring to FIG. 5 , in an embodiment, each of the plurality of cathodematerials 102 of the metal-air battery may have a flat panel shape. Theplurality of cathode materials 102 having the flat panel shape may bearranged in parallel. In one embodiment, for example, each of theplurality of cathode materials 102 having the flat panel shape may havea first side surface and a second side surface which are two oppositeside surfaces having relatively large areas, and a third side surfaceand a fourth side surface, which extend between the first side surfaceand the second side surface, have areas smaller than those of the firstside surface and the second side surface, and are opposite to eachother. In such an embodiment, electrolyte films 103 may be disposed onthe first side surface and the second side surface having the relativelylarge areas of each of the plurality of cathode materials 102. However,the electrolyte films 103 are not limited to the first side surface andthe second side surface, and may be disposed on all of the first tofourth side surfaces. In such an embodiment, as shown in FIG. 5 , theplurality of cathode materials 102 may be arranged in a way such thatthe first and second side surfaces of one of two adjacent cathodematerials 102 face those of the other. In one embodiment, for example,in the cathode of FIG. 5 , when the metal-air battery is a lithium-airbattery and has a specific capacity of about 1,350 milliampere hours pergram (mAh/g the plurality of cathode materials 102 may have a height Hof about 12.5 micrometers (μm) and a thickness T of about 10 nm or less,the electrolyte films 103 may have a thickness of about 10 nm or less,spaces 105 may have a width D of about 20 nm which is greater than thesum of the thicknesses of electrolyte films 103 facing each other, andthe number of the cathode materials 102 per unit area may be about200,000 per square centimeter (/cm²).

FIG. 6 is a schematic partial perspective view of a cathode for ametal-air battery according to an alternative embodiment.

Referring to FIG. 6 , in an embodiment, each of the plurality of cathodematerials 102 may have a cylindrical or cone shape. In one embodiment,for example, each of the plurality of cathode materials 102 may includecarbon nanotubes (CNTs). In such an embodiment, the electrolyte films103 may be disposed on outer circumferential surfaces of the pluralityof cathode materials 102.

In such an embodiment, a metal oxide 106 may be formed on the outercircumferential surface of each of the plurality of cathode materials102 during a discharge operation of the metal-air battery having thecathode illustrated in FIG. 6 .

FIG. 7 is a cross-sectional view illustrating a metal oxide 106 formedduring a discharge operation of the metal-air battery of FIG. 6 , and achange in the locations of the electrolyte films 103 caused by the metaloxide 106.

Referring to FIG. 7 , while the discharge operation is conducted, themetal oxide 106 is grown on outer circumferential surfaces of each ofthe plurality of cathode materials 102 including carbon nanotubes. Whenthe metal oxide 106 is formed between the plurality of cathode materials102 and the electrolyte films 103, the electrolyte films 103 are pushedout by the metal oxide 106 away from the plurality of cathode materials102 in a direction perpendicular to the outer circumferential surfacesof the plurality of cathode materials 102. Thus, spaces 105 are filledwith the electrolyte film 103.

In such an embodiment, the plurality of cathode materials 102 may bearranged to be spaced apart from each other by a predetermined distanceto provide the spaces 105 between the electrolyte films 103 on twoadjacent cathode materials 102 after the outer circumferential surfacesof the plurality of cathode materials 102 are coated with theelectrolyte films 103. In one embodiment, for example, distances betweenthe plurality of cathode materials 102 and a thickness of theelectrolyte films 103 may be selected such that a volume of the spaces105 is the same as a maximum volume of the metal oxide 106 formed bycomplete discharging of the metal-air battery. As described above, thevolume of the spaces 105 may be 100 to 120% greater than the maximumvolume of the metal oxide 106.

In one embodiment, for example, where the metal-air battery 100 is alithium-air battery and has a specific capacity of about 1,350 mAh/g,each of the plurality of cathode materials 102 may have a diameter ofabout 150 nm or less, each of the electrolyte films 103 may have athickness of about 10 nm or less, and each of the spaces 105 may have awidth D greater than about 20 nm. Here, the width D of the spaces 105may be defined as the distance between electrolyte films 103 facing eachother in a direction connecting centers of two adjacent cathodematerials 102 when the metal oxide 106 is not formed. The plurality ofcathode materials 102 may be arranged at a density (the number thereofper unit area) greater than 10⁹/cm². In one embodiment, For example, theplurality of cathode materials 102 may be arranged at a density in arange of about 10⁹/cm² to about 4×10¹⁰/cm². A height of each of theplurality of cathode materials 102 may be in a range of about 13 μm toabout 17 μm, and controlled according to the number of cathode materials102 per unit area.

FIG. 8 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment. In anembodiment, as shown in FIG. 8 , the metal-air battery may include onlyone cathode layer 112 rather than a plurality of cathode materials 102.In such an embodiment, the metal-air battery may include a plurality ofholes 115 vertically passing through the cathode layer 112. In such anembodiment, electrolyte films 103 may be disposed along inner walls ofthe cathode layer 112. A cross-sectional structure of an embodiment ofthe metal-air battery having the cathode of FIG. 8 may be substantiallythe same as that shown in the cross-sectional view of FIG. 1 . In suchan embodiment, the plurality of holes 115 may completely extend from topto bottom surfaces of the cathode layer 112, and the electrolyte films103 inside the plurality of holes 115 may extend to a top surface of theanode metal layer 101.

During a discharge operation of an embodiment of the metal-air batteryhaving the cathode of FIG. 8 , a metal oxide 106 may be formed on eachof the inner walls of the cathode layer 112 that define the plurality ofholes 115. FIG. 9 is a cross-sectional view illustrating a metal oxide106 formed during a discharge operation of the metal-air battery of FIG.8 , and a change in the locations of electrolyte films 103, caused bythe metal oxide 106. Referring to FIG. 9 , during the dischargeoperation of the metal-air battery, the metal oxide 106 is grown on theinner walls of the cathode layer 112 that define the plurality of holes115. The metal oxide 106 is then interposed between the inner walls ofthe plurality of holes 115 and the electrolyte films 103. Theelectrolyte films 103 are pushed out by the metal oxide 106 in adirection toward the centers of the plurality of holes 115, and thusspaces 105 defined by the electrolyte films 103 inside the plurality ofholes 115 are filled with the electrolyte films 103.

In such an embodiment, a size of the plurality of holes 115 and athickness of the electrolyte films 103 may be determined in a way suchthat the empty space 105 surrounded by the electrolyte films 103 has asufficient area. For example, a diameter or a width of the plurality ofholes 115 may be at least twice the thickness of the electrolyte films103. More specifically, a cross-sectional area of the empty space 105 ineach of the plurality of holes 115 may be greater than or equal to thatof the metal oxide 106 on each of the inner walls that define theplurality of holes 115 after the metal oxide 106 is formed to a maximumsize. In an embodiment, where the volume of the empty space 105 is about40% of a total volume of the cathode layer 112, and when a specificcapacity of 1,350 mAh/g or less is realized, electrolytes of theelectrolyte films 103 may be retained in the metal-air battery 100without leaking out to the outside of the cathode, thereby securingcharging/discharging reversibility.

Although FIG. 8 illustrates an embodiment of the plurality of holes 115each having a tetragonal cross-section, the cross-sections of theplurality of holes 115 are not limited thereto.

FIG. 10 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment. FIG. 11is a schematic partial perspective view of a cathode for a metal-airbattery according to another alternative embodiment.

In an embodiment, each of a plurality of holes 115 may have a hexagonalcross-section as illustrated in FIG. 10 or a triangular cross-section asillustrated in FIG. 11 . Alternatively, each of the plurality of holes115 may have a cross-section having another polygonal shape.

In each of the cathodes of FIGS. 8 to 11 , if the metal-air battery is,for example, a lithium-air battery and has a specific capacity of about1,350 mAh/g, a thickness t of a portion of the cathode layer 112 betweenthe adjacent inner walls of two adjacent holes 115 may be about 8 nm,the electrolyte films 103 may have a thickness of about 10 nm or lesswhen the metal oxide 106 is not formed, and the cathode layer 112 mayhave a height of about 12.5 μm. In such an embodiment, a distance fromthe center of each of the plurality of holes 115 to one of the verticesof the electrolyte films 103 may be greater than about 24 nm. A densityof the plurality of holes 115 (number of holes 115 per unit area) in thecathode layer 112 may be greater than 10⁹/cm². In one embodiment, forexample, the plurality of holes 115 may be arranged at a density in arange of about 10⁹/cm² to about 10¹⁰/cm².

FIG. 12 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment.

Referring to FIG. 12 , each of a plurality of holes 115 defined througha cathode layer 112 may have a round or circular cross-section. In suchan embodiment, electrolyte films 103 may be disposed on or to cover theinner walls of the cathode layer 112 that define the round holes 115.

FIG. 13 is a cross-sectional view illustrating a metal oxide 106 formedduring a discharge operation of a metal-air battery of FIG. 12 , and achange in the locations of electrolyte films 103, caused by a metaloxide 106.

In such an embodiment, where each of the plurality of holes 115 has around cross-section, each of the electrolyte films 103 have across-section having a round ring shape, and the metal oxide 106 formedon the inner walls of the holes 115 may also have a cross-section havingthe round ring shape. In such an embodiment, when the metal oxide 106 isformed through the discharge operation of the metal-air battery, theelectrolyte films 103 are pushed out toward centers of the round holes115. Spaces 105 in the holes 115 may be partially or completely filledwith the electrolyte films 103 when the metal oxide 106 is formed to amaximum size. When the spaces 105 are completely filled with theelectrolyte films 103, the electrolyte films 103 may have the same roundcross-section as the electrolyte films 103.

A diameter of the round holes 115 and a thickness of the electrolytefilms 103 may be determined in a way such that the spaces 105 surroundedby the electrolyte films 103 have a sufficient area. In one embodiment,for example, the area of the cross-section of the space 105 may begreater than or equal to that of the cross-section of the metal oxide106 formed to a maximum size on the inner wall of each of the roundholes 115.

FIG. 14 is a schematic partial perspective view of a cathode for ametal-air battery according to another alternative embodiment.

In an embodiment of FIG. 12 , the round holes 115 are arranged in anarray having a tetragonal shape pattern but a pattern of the arrangementof the round holes 115 is not limited thereto. In one alternativeembodiment, for example, as shown in FIG. 14 , a plurality of roundholes 115 may be arranged in an array having a hexagonal shape pattern.Alternatively, a plurality of round holes 115 may be arranged in arrayshaving various other patterns.

In each of the cathodes shown in FIGS. 12 to 14 , if the metal-airbattery is, for example, a lithium-air battery and has a specificcapacity of about 1,350 mAh/g, a thinnest portion of the cathode layer112 between two adjacent round holes 115 may have a thickness in a rangeof about zero (0) nm to about 4 nm, the electrolyte films 103 may have athickness of about 10 nm when the metal oxide 106 is not formed, and thecathode layer 112 may have a height of about 12.5 μm. In such anembodiment, a radius of the space 105 may be greater than about 34 nm.Here, the radius of the space 105 may be defined as the distance fromthe center of each of the plurality of round holes 115 to a surface ofeach of the electrolyte films 103. A density of the plurality of roundholes 115 formed in the cathode layer 112 (number of round holes 115 perunit area) may be about 4×10¹⁰/cm².

FIGS. 15 to 17 are graphs showing characteristics of an embodiment ofthe metal-air battery of FIG. 6 . In FIGS. 15 to 17 , it is assumed thatthe metal-air battery is a lithium-air battery and has an areal capacityof 1.35 mAh/cm², the plurality of cathode materials 102 have a densityof 2 g/cm³, and the electrolyte films 103 have a density of 1 g/cm³. Thegraph of FIG. 15 shows a specific capacity of the metal-air batteryaccording to a diameter of the plurality of cathode materials 102 and anelectrolyte-to-cathode weight ratio when the thickness of theelectrolyte films 103 was 10 nm. The graph of FIG. 16 shows a thicknessof the electrolyte films 103 according to a diameter of the plurality ofcathode materials 102 and an electrolyte-to-cathode weight ratio. Thegraph of FIG. 17 shows a height of the plurality of cathode materials102 according to a diameter of the plurality of cathode materials 102and an electrolyte-to-cathode weight ratio. FIGS. 15 to 17 illustratethat the plurality of cathode materials 102 each having a cylindricalshape are arranged in an array of a tetragonal pattern.

Referring to the graphs of FIGS. 15 to 17 , when the thickness of theelectrolyte films 103 was controlled to be about 20 nm or more and thediameter of each of the plurality of cathode materials 102 having thecylindrical shape was 30 nm, a maximum specific capacity of themetal-air battery was about 750 mAh/g and a weight of the electrolytefilms 103 was about three times than that of the plurality of cathodematerials 102.

FIGS. 18 to 20 are graphs showing characteristics of an embodiment ofthe metal-air battery of FIG. 14 .

In FIGS. 18 to 20 , it is assumed that the metal-air battery is alithium-air battery and has an areal capacity of 1.35 mAh/cm², thecathode layer 112 has a density of 2 g/cm³, and the electrolyte films103 have a density of 1 g/cm³. The graph of FIG. 18 shows a specificcapacity of the metal-air battery according to a diameter of theplurality of holes 115 and an electrolyte-to-cathode weight ratio whenthe thickness of the electrolyte films 103 was 10 nm. The graph of FIG.19 shows a thickness of the electrolyte films 103 according to adiameter of the plurality of holes 115 and an electrolyte-to-cathodeweight ratio. The graph of FIG. 20 shows a height of the cathode layer112 according to a diameter of the plurality of holes 115 and anelectrolyte-to-cathode weight ratio. In the graphs of FIGS. 18 to 20 ,regions indicated by oblique lines represent regions in whichelectrolytes of the electrolyte films 103 leak to the outside of themetal-air battery due to an insufficient size of the space 105 in eachof the plurality of holes 115 during a discharge operation of themetal-air battery.

Referring to the graphs of FIGS. 18 to 20 , a thickness of theelectrolyte films 103 may be desired to be about 50 nm and a weight ofthe electrolyte films 103 may be desired to be about three times that ofthe cathode layer 112 when the plurality of holes 115 have a diameter ofabout 200 nm, and a maximum specific capacity of about 750 mAh/g may beachieved.

A cathode for a metal-air battery and a metal-air battery including thesame have been described above with reference to the embodimentsillustrated in the drawings, but they are merely examples. It would beapparent to those of ordinary skill in the art that various changes maybe made thereto without departing from the principles and spirit of theinventive concept, the scope of which is defined in the claims and theirequivalents. It should be understood that the embodiments describedherein should be considered in a descriptive sense only and not forpurposes of limitation. Descriptions of features or aspects within eachembodiment should typically be considered as available for other similarfeatures or aspects in other embodiments.

What is claimed is:
 1. A cathode for a metal-air battery, the cathode comprising: a plurality of cathode materials, each of the plurality of cathode materials having a cylindrical or cone shape and using oxygen as an active material; and a plurality of electrolyte films, each of the plurality of electrolyte films being disposed on an outer circumferential surface of a corresponding one of the plurality of cathode materials; wherein a space, which is not occupied by the plurality of cathode materials and the plurality of electrolyte films, is defined between the plurality of electrolyte films, wherein the plurality of cathode materials is spaced apart from each other by a predetermined distance, wherein each of the plurality of cathode materials has a diameter of 150 nm or less, and wherein each of the plurality of electrolyte films has a thickness of 10 nm or less.
 2. The cathode of claim 1, wherein the plurality of electrolyte films are formed of an organic material.
 3. The cathode of claim 1, wherein a volume of the space is equal to or less than 120% of a predetermined volume.
 4. The cathode of claim 1, wherein a distance between adjacent electrolyte films, among the plurality of electrolyte films, facing each other in a direction connecting centers of two adjacent cathode materials, among the plurality of cathode materials, is greater than 20 nm.
 5. The cathode of claim 1, wherein the plurality of cathode materials are regularly arranged.
 6. The cathode of claim 1, wherein each of the plurality of cathode materials comprises carbon nanotubes.
 7. The cathode of claim 1, wherein the plurality of cathode materials are arranged at a density greater than about 10⁹/cm².
 8. A metal-air battery comprising: a cathode comprising a plurality of cathode materials and a plurality of electrolyte films, each of the plurality of cathode materials having a cylindrical or cone shape and using oxygen as an active material, and each of the plurality of electrolyte films being disposed on an outer circumferential surface of a corresponding one of the plurality of cathode materials; an anode metal layer configured to supply metal ions to the plurality of cathode materials; and a gas diffusion layer configured to supply oxygen to the plurality of cathode materials, wherein a space, which is not occupied by the plurality of cathode materials and the plurality of electrolyte films, is defined between the plurality of electrolyte films, wherein the plurality of cathode materials is spaced apart from each other by a predetermined distance, wherein a volume of the space is greater than or equal to a maximum volume of a product formed between each of the plurality of cathode materials and a corresponding one of the plurality of electrolyte films during a discharge of the metal-air battery, wherein each of the anode metal layer and the gas diffusion layer has a flat panel form and the anode metal layer and the gas diffusion layer are disposed in parallel to each other, wherein the plurality of cathode materials are arranged between the anode metal layer and the gas diffusion layer to be perpendicular to a surface of the anode metal layer wherein each of the plurality of cathode materials has a diameter of 150 nm or less, and wherein each of the plurality of electrolyte films ahs a thickness of 10 nm or less.
 9. The metal-air battery of claim 8, wherein the volume of the space is equal to or less than 120% of the maximum volume of the product.
 10. The metal-air battery of claim 8, wherein a distance between adjacent electrolyte films facing each other in a direction connecting centers of two adjacent cathode materials is greater than 20 nm.
 11. The metal-air battery of claim 8, wherein each of a plurality of electrolyte films of the cathode comprises: a first electrolyte portion disposed on a top surface of the anode metal layer; and a second electrolyte portion extending from the first electrolyte portion to the outer circumferential surface of one of the plurality of cathode materials.
 12. The metal-air battery of claim 11, further comprising a third electrolyte portion which transmits metal ions and blocks moisture and oxygen, wherein the third electrolyte portion is disposed between the first electrolyte portion and the anode metal layer.
 13. The metal-air battery of claim 8, wherein the plurality of electrolyte films are formed of an organic material.
 14. The metal-air battery of claim 11, wherein the plurality of cathode materials are arranged in a way such that each of first end portions thereof is in contact with a corresponding one of the first electrolyte portions and second end portions thereof are in contact with the gas diffusion layer.
 15. The metal-air battery of claim 8, wherein the plurality of cathode materials are regularly arranged.
 16. The metal-air battery of claim 8, wherein each of the plurality of cathode materials comprises carbon nanotubes.
 17. The metal-air battery of claim 8, wherein the plurality of cathode materials are arranged at a density greater than about 10⁹/cm². 